1. Field of the Invention
The present invention generally relates to controlling a dimming of various types of lamps. The present invention specifically relates to hindering discontinuities and oscillations within a lamp due to the ionization and recombination time delay of the lamp during steady state operation.
2. Description of the Related Art
FIGS. 1 and 4 illustrates a known structural arrangement of a universal lamp driver 20 including a N-depletion metal oxide semiconductor field-effect transistor (xe2x80x9cMOSFET 1xe2x80x9d), a N-depletion metal oxide semiconductor field-effect transistor (xe2x80x9cMOSFET 2xe2x80x9d), a capacitor C1, an inductor L1, and a capacitor C2 for providing a lamp voltage VL and a lamp current IL to lamp 10 in response to a source supply voltage VSS and a source supply current ISS. FIG. 1 further illustrates a conventional multiplier 30 and a known structural arrangement of a feedback compensation circuit 40 having a conventional gate driver 41, a conventional pulse width modulator 42, a comparator in the form of an operational amplifier (xe2x80x9cOP AMP 1xe2x80x9d), a capacitor C3, and a resistor R2. Multiplier 30 computes and provides a lamp power signal LPS to feedback compensation circuit 40 that is indicative of lamp voltage VL and lamp current IL. In response to lamp power signal LPs and a reference voltage VREF, feedback compensation circuit 40 controls an active mode of operation of MOSFET 1 and an active mode of operation of MOSFET 2 whereby lamp current IL can be adjusted to thereby adjust a dimming level of lamp 10.
An advantage of universal lamp driver 20 is the ability to drive various forms of lamp 10 (e.g., any type of gas discharge lamp). A disadvantage of feedback compensation circuit 40 is the inability to control an adjustment of lamp current IL for all types of various forms of lamp 10. FIG. 2 illustrates the inability of feedback compensation circuit 40 to control an adjustment of lamp current IL within an inaccessible area. The result is a discontinuity in lamp current IL as illustrated in FIG. 3A.
FIG. 4 illustrates a rectifier 50 and a known structural arrangement of a feedback compensation circuit 60 having a conventional gate driver 61, a conventional voltage controlled oscillator 62, a comparator in the form of an operational amplifier (xe2x80x9cOP AMP 2xe2x80x9d), a capacitor C4, a capacitor C5, a resistor R3, and a resistor R4. Rectifier 50 computes and provides lamp power signal LCS to feedback compensation circuit 60 that is indicative of lamp current IL. In response to lamp current signal LCS and reference voltage VREF, feedback compensation circuit 60 controls an active mode of operation of MOSFET 1 and an active mode of operation of MOSFET 2 whereby lamp current IL can be adjusted while experiencing a continuity as illustrated in FIG. 3B.
However, a disadvantage of feedback compensation circuit 60 is the inability to provide a compensation to half-bridge universal lamp driver 20 that is adapted to a particular type of lamp 10. The result is an instability problem of lamp driver 20 for some types of lamp 10. For example, feedback compensation circuit 60 can be designed to provide a 2 pole-1 zero compensation with a zero at 200 rad/sec and a pole at 10 rad/sec. Consequently, lamp current IL can be unstable as illustrated in FIG. 5A when lamp 10 is a type of lamp having a time constant of 50 xcexcs during steady state operation, and lamp current IL can be stable as illustrated in FIG. 5B when lamp 10 is a type of lamp having a time constant of 500 xcexcs during steady state operation.
The present invention addresses the shortcomings of the prior art.
The present invention relates to an adaptive control of universal lamp drivers. Various aspects of the present invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
One form of the present invention is a method of adaptively controlling a lamp driver coupled to a lamp. First, a time constant corresponding to the lamp is determined. Second, the lamp driver is operated to provide a lamp current to the lamp as a function of the time constant of the lamp.
A second form of the present invention is a device comprising a lamp driver and an adaptive compensation circuit. The lamp driver is operable to provide a lamp current to a lamp. The adaptive compensation circuit is operable to control the lamp current as a function of a time constant of the lamp.
The foregoing forms and other forms, features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.